In a well-known form of silent chain, each toothed link plate has a pair of teeth and a pair of pin holes. The link plates are disposed in alternating guide rows and link rows. The connecting pins are fixed to pin holes in guide plates disposed at both ends of each guide row on the outermost sides of chain. The pins fit loosely in pin holes in the toothed link plates so that the chain can flex and bend around sprockets.
In accordance with another aspect of the invention, the link plate teeth are shaped so that the inside surface of the rear tooth of each inner link plate comes into contact with a sprocket tooth on engagement with the sprocket, and the inside surface of the front tooth of each inner link plate is contact with a sprocket tooth on disengagement.
As shown in FIG. 5, in a conventional chain transmission, as a link plate 500 engages with a sprocket tooth 551, surfaces of the tooth heads of the chain first contact the tooth heads of the sprocket and slide along the tooth surfaces of the sprocket. By reason of its sliding action, a silent chain has a smaller impact compared to that of a roller chain or a bushing chain, and suppresses noise. Initial engagement can take place between a sprocket tooth and an inside tooth surface of a link plate, or between a sprocket tooth and an outside surface of a link plate. Improvements in tooth forms have been proposed to reduce impact, and examples of such improvements are described in United Stated patent publication 2009/0156342, published Jun. 18, 2009.
FIGS. 6(a) and 6(b) are enlarged views of an area VI in FIG. 5 at the location of engagement of a link plate 500 of a conventional silent chain with a sprocket 550, the views pertaining respectively to a chain transmission in which initial engagement is between an inside link plate surface and a sprocket tooth, and an alternative chain transmission in which initial engagement is between an outside link plate surface and a sprocket tooth.
As shown in FIG. 6(a), when an inside surface of a tooth 501 of the link plate 500 engages with, or disengages from, a sprocket tooth, tension T2 in the silent chain, and force T1 at the point of contact between a sprocket tooth and a link plate tooth change rapidly, inevitably generating impact noise.
Moreover, as shown in FIG. 6(a), when an inside surface of a plate tooth first engages a sprocket tooth or disengages therefrom, a drag T′1 corresponds to the force T1. A large component Tr of the drag T′1 generates a moment Tr·R1, which rotates the link plate 500 toward the sprocket about the axis of the connecting pin 520. Furthermore, as shown in FIG. 6(b), when the outside surface of a plate tooth first engages the sprocket tooth or disengages therefrom, a component Tr of drag T′1 corresponding to the force T1 applied at the point of contact also rotates the link plate toward the sprocket about connecting pin 520. This force Tr, as shown in FIG. 6(b), is smaller than the force Tr in FIG. 6(a). However, the radius R2 between the connecting pin and the contact point is larger than the radius R1 in FIG. 6(a). Therefore the moment Tr·R2 is comparable in magnitude to moment Tr·R1 in FIG. 6(a). Thus, the force components Tr become factors that contribute to vibration in the free span of the chain that travels between sprockets. At the same time, the force component Tp at the contact point and extending toward the connecting pin 520 increases. As a result, there was a problem of impact noise due to rapid changes in the chain tension T2, and in the force T1 applied at the contact point.
An object of this invention is to provide a silent chain transmission, which prevents rapid changes in the force applied at the point of contact between a sprocket tooth and a plate tooth of the chain on engagement and disengagement, and also prevents rapid changes in chain tension, so that noise generated in the operation of the chain transmission is reduced by reducing impact noise and suppressing vibration.